1. The Field of the Invention
This invention relates to devices for dispensing a plurality of fluids in a precise ratio to each other. More particularly, the invention disclosed herein relates to an improved fluid-driven liquid proportioning pump that effects the positive displacement in a precise ratio of an externally pressurized drive fluid and one or more constituent fluids. While adaptable to a number of diverse uses, the methods and apparatus of the present invention have ready applicability in the field of mixing and dispensing beverages.
2. Background Art
Many aspects of industrial processing and consumer merchandising require the continuous, precise dispensing and simultaneous mixing of a plurality of constituent fluids into a desired product. This is the case in the manufacture of paints, pesticides, fertilizers, and industrial sealants, as well as in the preparation of cosmetics, pharmaceuticals, toothpaste, and even foods, such as margarine, syrups, and beverages.
While the methods and apparatus of the present invention finds utility in each of the above-named and other fields, an immediate application of the present invention resides in meeting the demand in the beverage industry for an improved manner by which the constituent fluids of beverages may be dispensed and mixed into a consumer product within the narrow specifications that are dictated by consumer tastes. Such beverages may be of both the carbonated and the non-carbonated variety.
In the retail area the dispensing of individual constituent fluids for mixture into a final consumable product is prominent in relation to the retailing of carbonated and other syrup-based beverages and juices. This occurs in restaurants and fast food establishments, at entertainment and sport events, and at grocery stores, where purchases of customer-dispensed beverages is on the rise.
In the production of cola-type beverages, orange and other fruit drinks, lemonade, and the like, aromatic flavoring agents in liquid form, such as syrups and concentrates, are metered and combined with predetermined quantities of carbonated or plain water. Typically, the water is pressurized and mixed with the syrups to form a finished beverage that may be dispensed either into reusable or disposable containers.
This process of dispensing and blending into a final mixture the proper quantities of each fluid in a manner capable of satisfying the sensitized tastes of the consuming public has been rendered more complicated in recent years by two developments. First, the public preference for artificially sweetened carbonated beverages has increased dramatically. Second, the perceived necessity to replace the artificial sweetener saccharin with another has resulted in a widespread shift by the food industry to the use of the artificial sweetener, aspertaime, which is commonly marketed under the trademark NUTRASWEET.RTM.. Unfortunately, aspertaime has a relatively short shelf life, after which the flavor of the sweetener undergoes markedly noticeable alteration.
This fact about aspertaime has lead to the practice in the soft drink industry of separating the sweetening element from the aromatic syrups, so that the turnover of sweetener supplies can be accelerated. Accordingly, in dispensing and blending the components of a carbonated beverage that is to contain aspertaime, it is now necessary to blend, not merely two different constituent fluids, but three: water, an aromatic syrup, and an artificial sweetener.
The effort to develop fluid proportioning devices suitable for metering more than two constituent fluids has cast in a harsher light the drawbacks of the devices previously developed toward the dispensing of only two constituent fluids.
Prior devices were complicated, requiring plural conduits, complex valving, and forms of involved linkages for effecting coordination between the operation of otherwise independent dispensing mechanisms. Devices which failed to physically integrate the dispensing mechanisms necessitated the use of additional mechanical system for coordinating the necessarily separate dispensing functions. This added to the complexity of dispensing devices, resulting in a need for increased maintenance. The resort to electrical drive motors as a source of motive power for the prior devices only complicated the proportioning pumps by adding thereto another system needing its own separate maintenance and isolation for safety and operational purposes.
Many proportioning pumps were reciprocating in nature, but were successful in dispensing all of the constituent fluids in only one direction of their reciprocating motion. This produced uneven flow and irregular ratios of the constituent fluids involved in each cycle of operation.
The actual proportioning aspect of such devices presented several problems. Many simply were not accurate, so that a user was faced with unreliability in preparing a final product. The proportioning function was frequently effected by valving external to the mechanism with which the constituent fluids were actually advanced through the system. Such external valving itself comprised a separate system of mechanical operation requiring its own maintenance and coordination.
A significant problem in prior proportioning pumps was the number of dynamic seals required to segregate the plurality of fluids involved, to preserve pressure in the device, and to prevent fluid leakage. In many cases, of necessity, one or more of these seals was exposed on one side to the atmosphere, tending to age such seals rapidly due to drying. The concomitant need for replacement and repair of such components is readily predictable.
The reliability of numerous prior proportioning pumps has been impaired by the entrapment of air bubbles within the chambers and fluid passageways thereof. Air bubbles would not of themselves impair reliability, if the air bubbles could be successfully induced to move through and out of the proportioning pump with the flowing constituent fluids. Air bubbles tend to rise to the highest point within a proportioning pump and accumulate there. Thus, both the internal design of proportioning pumps and the orientation of the mounting thereof to fixed surfaces at the location of use have tended to defeat the desirable objective of purging the proportioning pumps of air bubbles during normal use.
Some proportioning pumps have accordingly been supplied with air bubble venting stop cocks that communicate with the highest points in various chambers and fluid passageways in the proportioning pump. Through periodic operation of these venting stop cocks, entrapped air is in theory removed. Disadvantageously, however, venting stop cocks increased the complexity of proportioning pumps, the tendency to leak, and the need for additional maintenance activity, if only that of manually operating the stop cocks on a periodic basis.
Ultimately, prior fluid proportioning pumps were complicated assemblages of separate mechanical systems. Each separate component system required its own maintenance. Intervening systems were necessary for effecting coordinated operations. In the effort to streamline such devices, designers were faced with two conflicting tendencies. The subsystems additional to that used to advance constituent fluids could be located external to the advancement system, where they would be relatively easily accessible for maintenance and adjustment purposes but relatively difficult to coordinate in any simple manner. Alteratively, such additional subsystems could be integrated into the mechanical structure of the fluid advancement subsystem rendering them difficult to access, while possibly more easy to coordinate.
All such drawbacks existed in proportioning pumps used with just two constituent fluids. The need for proportioning pumps which could effectively dispense more than two fluids exacerbated known problems. Additional constituent fluids require additional subsystems for coordination and proportioning. Devices grew more complex, rather than simpler, as would have been desired.
One method and apparatus which coped effectively with additional constituent fluids and simplified the number of subsystems and components involved is disclosed in U.S. Pat. No. 5,058,768, which will be referred to hereinafter as the '768 Patent.
In the '768 Patent a fluid-driven proportioning pump is illustrated that dispenses precise volumes of at least three different constituent fluids, including among them a pressurized drive fluid. The proportioning pump comprises a drive cylinder made up of a tube closed at each end by a plate assembly. A correspondingly formed drive piston is disposed in the drive cylinder, dividing the drive cylinder into first and second drive fluid chambers. The drive piston is propelled in a reciprocating motion alternately toward each of the drive fluid chambers by the pressurized drive fluid itself. Passageways for admitting the drive fluid into and removing drive fluid from each of the drive fluid chambers are formed in the end plate assemblies that effect closure of the tube of the drive cylinder.
Each face of the drive piston is provided with a projecting proportioning piston corresponding to each of the non-pressurized constituent fluids. These proportioning pistons extend into corresponding proportioning cylinders that open into each fluid drive chamber toward the drive piston. Passageways into and out of each of the proportioning cylinders are formed in the end plate assemblies that effect closure of the tube of the drive cylinder.
A valving mechanism housed entirely within the drive cylinder regulates the flow of the drive fluid into and out of the drive fluid chambers on opposite sides of the drive cylinder. The valving mechanism passes rigidly through the reciprocating drive piston into value bores in each of the two opposed end plate assemblies. While the economy of mechanisms resulting from this valving mechanism is advantageous, the valving mechanism requires extremely precise alignment among the valving mechanism, the drive piston, and the two end plate assemblies of the device. Otherwise, the valving mechanism and the drive piston in undertaking to move in the respective roles of each, experience unacceptable levels of binding stress that reduces efficiency and can even prevent the desired operation of the device. This places severe constraints on the assembly precision required in manufacturing the proportioning pump disclosed in the '768 Patent.
An over-center mechanism activated by movement of the drive piston at the extremes of the strokes of the reciprocating motion thereof operates the valving mechanism and admits the pressurized drive fluid into alternate of the drive fluid chambers. The over-center mechanism is activated by system of loop springs disposed in each of the first and second drive fluid chambers and retained in different degrees of compression between the drive piston and the valving mechanism. The degree of compression in the system of loop springs varies continuously according to the position of the drive piston during the reciprocating movement thereof. This arrangement in the proportioning pump of the '768 Patent, while found to be an improvement over earlier prior proportioning devices, is still somewhat sluggish in responsiveness, particularly in any initial operation of the proportioning pump after a prolonged period of dormancy.
In the proportioning pump disclosed in the '768 Patent selective adjustment of the proportion among the drive fluid and the other constituent fluids is enabled from the exterior of the proportioning pump through the use of a complicated mechanical system. This proportioning adjustment system requires, however, that the proportioning pistons to be configured as disk-like piston heads that are slidably mounted on a turnable shaft that projects from the end face of the drive piston. The shaft has an enlarged head on the side of the disk remote from the drive piston. The head of the shaft is provided with a fitting that is manipulatable from the outside of the proportioning pump by built-in retractable tools that are provided for each distinct proportioning piston head. All elements of the proportioning adjustment system are advantageously contained within the proportioning pump.
While this arrangement affords the convenience of post-assembly adjustments to the portion among the drive fluid and other constituent fluids, the result is extremely complex mechanically, increasing dramatically the number of differing parts required in the assembly of the proportioning pump. Access to the interior of the proportioning pump for this purpose, much like the introduction of air bubble venting stop cocks, not only increases the complexity of the proportioning pump itself, but the tendency thereof to leakage.
One unexpected disadvantage of an externally adjustable proportioning adjustment system is a tendency for a proportioning pump set at a predetermined desired portion among the drive fluid and constituent fluids dispensed therefrom to deviate from that predetermined proportion during use. As a result, periodic testing of the proportions among those fluids in the output is required, and concomitantly periodic recalibration of the proportioning pump. Thus, a proportioning pump such as that disclosed in the '768 Patent which must be fine-tuned after manufacture, is one which demands ongoing related maintenance activity.
The drive fluid passageways and constituent fluid passageways formed in each end plate of the proportioning pump disclosed in the '768 Patent necessitate the attachment to that proportioning pump of at least four hoses for the drive fluid, as well as four hoses for each of the other individual constituent fluids. For each single fluid an input and an output hose must be connected to the end plate assembly on each end of the drive piston. For a single drive fluid and a pair of constituent fluids, twelve hose couplings are thus required.
Difficulties have been encountered due to competing requirements relative to the structure and material composition of which the tube of a proportioning pump is comprised. The first and second drive fluid chambers housed within that tube are separated from each other by the reciprocating drive piston. The circumference of the drive piston is fitted with an encircling sealing ring that effects the actual sealing and sliding contact with the inner walls of that tube.
When introduced into the drive cylinder one effect of the pressurized drive fluid is to distort the shape of the tube of the drive piston. This produces two adverse effects. First, the desired ratio between the drive fluid and one or both of the other constituent fluids is altered. Secondly, changes in the shape of the drive cylinder can impair the seal effected by the sealing ring on the drive piston with the inner walls of the tube of the pump.
Efforts to rigidify the tube of the drive cylinder against the effects of the pressure of the drive fluid have been numerous. Each has proved unsuccessful for distinct reasons.
The walls of the tube of the drive cylinder have, for example, been thickened dramatically resulting in a more rigid structure, but also in a more bulky device that, by consuming substantial quantities of constituent material, is expensive to manufacture. Alternatively, the thickness of the walls of the tube of the drive cylinder has been maintained at an acceptable size by forming the tube of the drive cylinder from a very strong material. If in the process a castable material is used such as steel, then the cost of manufacturing the device is still quite high.
On the other hand, efforts toward the same end have been made using inexpensive moldable materials such as resins, but to achieve adequate strength in the device these materials quire reinforcement, usually by adding thereto a matrix of reinforcing fibers. This has resulted in a marked roughening of the inner surface of the tube of the drive cylinder. Correspondingly, abrasion of the sealing ring on the reciprocating drive piston has increased, along with the need for remedial maintenance.